1. Field of the Invention
The present invention relates to a technique capable of equalizing voltages across both terminals of the respective series-connected storage elements in such a manner that energy is transferred among a plurality of series-connected storage elements which are mounted on an electric automobile, an energy-hybrid type vehicle, and various sorts of systems capable of using storages of electric energy.
2. Description of the Related Art
Japanese Laid-open Patent Application No. Hei-8-214454 and U.S. Pat. No. 5,594,320 discloses voltage equalizer circuits.
Generally speaking, a voltage equalizer circuit disclosed in these publications is referred to as a xe2x80x9cflyback type voltage equalizer circuit.xe2x80x9d As indicated in FIG. 8, the flyback type voltage equalizer circuit is equipped with a transformer having a plurality of secondary windings n2 to n4; a switch SW1 connected to a primary winding n1 of this transformer T1; a plurality of rectifying circuits CR1, CR2, CR3 connected to the respective secondary windings n2, n3, n4 of the transformer T1; and charging circuits for connecting outputs of the respective rectifying circuits in each of unit cells. In this flyback type voltage equalizer circuit, constant electric power outputs of the respective secondary windings are rectified which are obtained by switching the primary winding of the transformer by the switch SW1, and then, each of the unit cells of capacitor batteries C1, C2, C3 which are constituted to be series-connected to each other is charged by the constant electric power outputs. As a result, when a battery voltage of a unit cell is low, a charge current becomes large, whereas when a battery voltage of a unit cell is high, a charge current becomes small, so that a plurality of series-connected battery voltages can be automatically and equally charged to the capacitor batteries.
In such a flyback type voltage equalizer circuit, while such a cycling operation between the charging operation and the discharging operation is repeatedly carried out by the switch, since the electric power is supplied from the power supply side every time switching operation is performed, the battery voltage is increased. Even when the battery voltage is reached to a predetermined voltage value, since the switching operation is continued, the resulting battery voltage is more and more increased, and finally, the battery may be brought into the overcharge condition. Such a flyback type voltage equalizer circuit necessarily requires the circuit capable of preventing the overcharge condition, and therefore, owns such a problem that the entire circuit thereof becomes complex and is manufactured in high cost.
Also, generally speaking, the voltage equalizer circuit described in the above-described U.S. Pat. No. 5,594,320 is referred to as a forward type voltage equalizer circuit. As shown in FIG. 9, in this forward type voltage equalizer circuit, a plurality of closed circuits are arranged in such a manner that each of batteries constituted by series-connecting a plurality of cells 11, 12, 60, 61, each of plural windings 67 to 70, and each of plural first switching elements 72 to 75 are series-connected to each other. Since all of these switching elements 72 to 75 are turned ON/OFF in the synchronous manner, a charging operation is carried out from a battery having a high cell voltage into a battery having a low cell voltage. As a result, voltages among the terminals of the respective cells may be equalized.
Such a forward type voltage equalizer circuit may have a function capable of equalizing the respective terminal voltages of these plural battery cells. However, the equalized voltages become the averaged voltage (correctly speaking, voltage equivalent to such a condition that battery energy is averaged) of the respective battery voltages, so that the battery voltage cannot be converged to the target voltage. Also, since the equalizer itself does not own the charging function, when the equalizing operation is continued, the discharge operation of the battery is carried out by the energy loss consumed by this equalizer. As a result, there is a risk that the battery may be brought into the over discharge condition.
The present invention has been made to solve the drawbacks of the above-explained flyback type voltage equalizer circuit and forward type voltage equalizer circuit, and therefore, has an object to provide a voltage equalizer apparatus for storage elements, capable of converging voltages among terminals of a plurality of series-connected storage elements to a final target value, while equalizing operation is carried out without occurrences of overcharging operation and of overdischarging operation.
To solve the above-described problem, according to an aspect of the present invention, in such a voltage equalizer apparatus in which each of plural windings electromagnetically coupled to each other, each of plural storage elements series-connected to each other, and each of plural first switching elements are connected to each other in a series connecting manner so as to constitute a plurality of closed circuits, a reference voltage winding electromagnetically coupled to the plurality of windings is provided; both a DC power supply and a second switching element are series-connected to the reference voltage winding; and all of the plural first switching elements and the second switching element are turned ON/OFF in a synchronous manner. As a consequence, the terminal-to-terminal voltages of the plural storage elements which are series-connected to each other can be converged to a final target value without risks of overcharging operation and overdischarging operation with respect to the storage elements, while performing the voltage equalizing operation.
Also, while the plural series-connected storage elements are series-connected to the DC power supply so as to constitute the voltage equalizer apparatus, the overall DC output may be connected to both an external power supply and an external load.
Also, since the output voltage of the DC power supply is variable, the terminal-to-terminal voltages of the plural series-connected storage elements may be converged to an arbitrary voltage.
Also, the DC power supply owns a bidirectional characteristic and is provided with an apparatus capable of supplying electric power to the plurality of series-connected storage elements, and also, capable of absorbing electric power supplied from the plurality of series-connected storage elements. As a result, the terminal-to-terminal voltages of the plural series-connected storage elements may be made lower than the present voltages.
Also, the voltage equalizer circuit comprises a voltage detecting section for detecting voltages among terminals of the plurality of series-connected storage elements; and the voltage of the DC power supply is set in response to an averaged terminal-to-terminal voltage of the storage elements, which is calculated from the voltage detecting section. As a result, since the terminal-to-terminal voltages of the storage elements can be gradually increased, the terminal-to-terminal voltages of the plural series-connected storage elements can be converged to the final target value without increasing the current capacities of the switching elements and also the capacity of the DC power supply.
It should be noted that when the storage elements are constituted by electric double layer capacitors, the allowable minimum voltage thereof is equal to a zero volt.
Also, the output voltage of the DC power supply is set between an allowable maximum voltage and an allowable minimum voltage, which are determined based upon a material of the storage element. As a result, the terminal-to-terminal voltages can be converged to the final target value, while neither a specifically-designed abnormal voltage detecting circuit, nor a protection circuit is provided with respect to the plural series-connected storage elements.
Also, according to another aspect of the present invention, in such a voltage equalizer circuit in which each of plural windings electromagnetically coupled to each other, each of plural storage elements series-connected to each other, and each of plural first switching elements are connected to each other in a series connecting manner so as to constitute a plurality of closed circuits, a reference voltage winding electromagnetically coupled to the plurality of windings is provided; both a DC power supply and a second switching element are series-connected to the reference voltage winding; a third switching element is provided so as to connect a monitoring storage element between series-connecting terminals of the reference voltage winding and the second switching element, and also so as to interrupt the connection between the DC power supply and the monitoring storage element; all of the plural first switching elements and the second switching element are turned ON/OFF in a synchronous manner; and the third switching element is turned OFF when a voltage between terminals of the monitoring storage element is monitored. As a result, an averaged terminal-to-terminal voltage of the plural series-connected storage elements can be readily detected.
Also, while the plural series-connected storage elements are series-connected to the DC power supply so as to constitute the voltage equalizer apparatus, the overall DC output may be connected to both an external power supply and an external load.
Also, since the DC power supply is capable of varying the voltage, the voltage of the DC power supply can be properly varied with reference to the detected averaged terminal-to-terminal voltage of the monitoring storage element. As a result, for instance, the terminal-to-terminal voltage of the plural series-connected storage elements can be converged to an arbitrary voltage without giving a load to the switching element.
Also, the DC power supply owns a bidirectional characteristic and is provided with an apparatus capable of supplying electric power to the plurality of series-connected storage elements, and also, capable of absorbing electric power supplied from the plurality of series-connected storage elements. As a result, in the case that the voltage of the DC power supply is set to be such a voltage lower than the detected averaged terminal-to-terminal voltage of the plural storage elements, the energy supplied from the plural storage elements is consumed on the side of the DC power supply, and thus the voltage of the DC power supply is continuously maintained at a low voltage. As a consequence, the terminal-to-terminal voltages of the plural series-connected storage elements can be converged to an arbitrary low voltage.
Also, the voltage equalizer circuit comprises a voltage detecting section for detecting a voltage between terminals of the monitoring storage element; and the voltage of the DC power supply is set in response to an averaged terminal-to-terminal voltage of the storage elements, which is calculated from the voltage detecting section. As a result, the voltage of the DC power supply can be properly set in correspondence with the current capacity of the switching element and the capability of the DC power supply.
Also, the output voltage of the DC power supply is set between an allowable maximum voltage and an allowable minimum voltage, which are determined based upon a material of the storage element. As a consequence, since a voltage applied to a storage element is limited between an allowable maximum voltage and an allowable minimum voltage, which are determined in accordance with a material and the like of this storage element, it is possible to prevent this storage element from being destroyed.
Also, in the case that a voltage between the terminals of the monitoring storage element during OFF time period of the third switching element exceeds a predetermined voltage, an external charging operation with respect to the plurality of series-connected storage elements is stopped and/or a warning notice is issued. As a result, such a fact that a voltage applied to a storage element is increased higher than, or equal to an overcharging voltage determined in accordance with the material of this storage element is notified to an operator, and furthermore, the equalizing operation is stopped, which can avoid that the voltage applied to the storage element is furthermore increased higher than the allowable maximum voltage.
Also, in the case that a voltage between the terminals of the monitoring storage element during OFF time period of the third switching element becomes lower than, or equal to a predetermined voltage, ON/OFF operations of the first switching elements and the second switching element are stopped and/or a warning notice is issued. As a result, for instance, such a fact that a voltage applied to a storage element is approximated to a discharge end voltage determined based upon the material of this storage element is notified to an operator, and the equalizing operation is stopped, which can avoid that the voltage applied to the storage element is furthermore decreased lower than the discharge end voltage.
Also, since the storage elements and/or the voltage monitoring storage element are electric double layer capacitors, such a capacitor having a large capacitance may be employed instead of a battery.
Also, since the third switching element is constituted by a relay, timing at which this relay is turned OFF can be easily controlled by an equalizer controller.
Also, according to another aspect of the present invention, in such a voltage equalizer circuit in which each of plural windings electromagnetically coupled to each other, each of plural storage elements series-connected to each other, and each of plural first switching elements are connected to each other in a series connecting manner so as to constitute a plurality of closed circuits, a reference voltage winding electromagnetically coupled to the plurality of windings is provided; both a DC power supply and a second switching element are series-connected to the reference voltage winding; a monitoring storage element is connected between series-connection terminals of the reference voltage winding and the second switching element; and a diode is provided which is biased along a forward direction in such a case that the voltage of the DC power supply is higher than a voltage between terminals of the monitoring storage element, so that the diode supplies a current to the reference voltage winding; and further, all of the plural first switching elements and the second switching element are turned ON/OFF in a synchronous manner. As a consequence, the voltage equalizing apparatus can be made simple in such a use case that the energy need not be extracted from the plural series-connected storage elements to the side of the DC power supply.
Also, while the plural series-connected storage elements are series-connected to the DC power supply so as to constitute the voltage equalizer apparatus, the overall DC output may be connected to both an external power supply and an external load.
Also, according to another aspect of the present invention, a voltage equalizer circuit of a storage element is featured by that at least a plurality of closed circuits in which each of plural windings electromagnetically coupled to each other, each of plural storage elements series-connected to each other, and each of plural first switching elements are connected to each other in a series connecting manner; while a reference voltage winding electromagnetically coupled to the plurality of windings, another closed circuit constituted by the reference voltage winding, a DC power supply, and a second switching element; and a controller for turning ON/OFF all of the first switching elements and the second switching element in a synchronous manner are formed in an integral body of a module. As a result, both a voltage and a current of a single module can be set as rated values. Since a plurality of modules are used, such a system having an arbitrary voltage and an arbitrary current capacity can be readily arranged.
Also, the DC power supply is constituted by a bidirectional converter; one of input/output terminals of the bidirectional converter is connected to the monitoring storage element; and the other of the input/output terminals of the bidirectional converter is connected to a battery. As a result, in the case that the voltage of the DC power supply is changed so as to lower the terminal-to-terminal voltages of the plural series-connected storage elements than the present voltages, since the energy can be easily absorbed (consumed), such a system capable of especially realizing an effective control can be obtained.
Also, since the plurality of storage elements are arranged by that storage elements having a plurality of charging/discharging characteristics different from each other are connected in a parallel connecting manner, it is possible to supply such currents suitable for load characteristics in transient states while the charging operation and the discharging operation are carried out.
Also, according to another aspect of the present invention, in such a voltage equalizer apparatus of a storage element in which each of plural windings electromagnetically coupled to each other, each of plural storage elements series-connected to each other, and each of plural first switching elements are connected to each other in a series connecting manner so as to constitute a plurality of closed circuits; a reference voltage winding electromagnetically coupled to the plurality of windings is provided; both a DC power supply and a second switching element are series-connected to the reference voltage winding; a third switching element is provided so as to connect a monitoring storage element between series-connection terminals of the reference voltage winding and the second switching element, and also so as to interrupt the connection between the DC power supply and the monitoring storage element; all of the plural first switching elements and the second switching element are turned ON/OFF in a synchronous manner; and the third switching element is turned OFF when a voltage between terminals of the monitoring storage element is monitored,
a voltage equalizing method of a storage element characterized in that; when a voltage between terminals of the storage element becomes such a value different from a target value by a predetermined voltage, or a higher voltage thereof, the plurality of storage elements are rapidly charged up to a predetermined charge voltage by a charging operation of an external power supply; and thereafter, both the first switching elements and the second switching element are turned ON/OFF so as to control the terminal-to-terminal voltage of the storage element to be equal to the target value. As a consequence, in the case that the terminal-to-terminal voltage of the storage element is low in such a case as when a system is initiated, and also this voltage becomes the value different from the target value by a predetermined voltage, the charging operation with respect to this storage element becomes short. As a result, after this storage element is quickly charged by the external power supply to the target value (preferably on the order of 95% of this target value, but not limited to this 95%), the equalizing operation is commenced. Thus, the storage element is gradually charged by way of the charging function of the voltage equalizer apparatus in such a manner that the charged voltage thereof is reached up to the target value, resulting in a rational charging operation.
Also, according to a further aspect of the present invention, in such a voltage equalizing apparatus of a storage element in which each of plural windings electromagnetically coupled to each other, each of plural storage elements series-connected to each other, and each of plural first switching elements are connected to each other in a series connecting manner so as to constitute a plurality of closed circuits; a reference voltage winding electromagnetically coupled to the plurality of windings is provided; both a DC power supply and a second switching element are series-connected to the reference voltage winding; a third switching element is provided so as to connect a monitoring storage element between series-connection terminals of the reference voltage winding and the second switching element, and also so as to interrupt the connection between the DC power supply and the monitoring storage element; all of the plural first switching elements and the second switching element are turned ON/OFF in a synchronous manner; and the third switching element is turned OFF when a voltage between terminals of the monitoring storage element is monitored,
a voltage equalizing method of a storage element characterized in that: when a voltage between terminals of the storage element becomes such a value different from a target value by a predetermined voltage, or a higher voltage thereof, the voltage of the DC power supply is set to such a voltage on the side of the target value and also in the vicinity of an averaged voltage of the monitored storage element; and while both the first switching elements and the second switching element are turned ON/OFF, a control operation is carried out in such a manner that the voltage of the DC power supply is gradually approximated to the target value. As a result, the terminal-to-terminal voltage of the storage element can be changed by a proper changing manner without any risk in correspondence with the current capacity of the switching element and also the performance of the DC power supply.